detection raycast too late

so i've been trying to use a raycast to detect the collision of my character on ground. I have the isGrounded=Raycast inside fixedUpdate. The detection however, happens every frame and not every physics step?

code:

using UnityEngine; using System.Collections;

public class Movement : MonoBehaviour {

 float direction = 1;
 float speed = 0.01f;
 float jumpHeight = 0.03f;
 float fallSpeed = 0.1f;
 bool isGrounded;
 float velx = 0;
 float vely = 0;
 
 void Update () {
     Move();

 }
 void FixedUpdate(){
     isGrounded = Physics2D.Raycast (transform.position, -Vector2.up,0.13f,~(1<<8));
 }
 void Move(){
     if (velx < -0.1f){
         transform.eulerAngles = new Vector2(0,180);
     }
     if (velx > 0.1f){
         transform.eulerAngles = new Vector2(0,0);
     }
     velx = direction * speed;

     if (isGrounded) {
         vely = 0;
         if (Input.GetButtonDown("Jump")) {
             vely = jumpHeight;
         }
     } else {
         vely -= fallSpeed * Time.deltaTime;
     }
         transform.Translate (new Vector2(velx,vely));
 }

}

any ideas?